Ranked in these QuestionsQuestion Ranking

Pros

Pro

Files are usable anywhere at anytime

Users are not tied to one service provider, program, platform, or database engine.

Pro

Ultimate flexibility

This app's flexibility is based on its minimalist approach, giving the user near-infinite freedom.

Pro

Agenda views

Pro

Absolutely free

Emacs with Org-mode is free as in beer and free as in speech – that is, it costs nothing and it’s totally open source.

Pro

Supports plaintext spreadsheets

Pro

There are a lot of extensions, for exporting to html, bootstrap, js-reveal and much more.

Pro

Incredibly extensible

There are many plug-ins for Org-mode, including Org-habits and Org-notify. If Org-mode lacks some piece of functionality, it is very easy to add it.

Cons

Con

Android app isn't very good

There are several user-created apps for Android, but none seem to offer the same level of functionality as other to-do apps.

Con

By default, a hard-to-read display

The default way of writing an outline or checklist creates a very messy wall of text that's difficult to read with no vertical spacing. You can manually add vertical spacing, but the Org operations don't preserve it. There are pretty-display modes, but you need to remember how to enable them, etc. etc.

Con

Unintuitive user interface

The key combinations are unintuitive and difficult to remember. This is probably because there are a lot of hidden "modes" depending on where the cursor is. Actions aren't paired with reversing actions like in other todo apps. For example, hitting shift-tab does NOT reverse the effect of hitting tab.